Citric acid, gluconic acid, and other materials have been used in the past to stabilize iron in solution and thus prevent its precipitation in forms such as ferric hydroxide and ferric oxide, wherein iron is in the third oxidation state. Citric acid and such materials effectively maintain iron in solution by forming complexes therewith which are soluble in water and thereby, remain dissolved in water. Although citric acid and cognate materials are effective as solubilizing agents for iron in solution, they are not antiscalants and are ineffective against scale such as calcium carbonate, calcium phosphate, calcium sulfate, magnesium hydroxide, and the like.
U.S. patent application entitled "Scale Inhibition In Water Systems" filed on Aug. 6, 1984, and bearing Ser. No. 638,158, was filed for inventors Amjad and Masler. That application matured into U.S. Pat. No. 4,566,973 which issued Jan. 28, 1986. U.S. Pat. No. 4,556,973 discloses the use of copolymers of an acrylic acid and a substituted acrylamide in an aqueous medium to reduce or inhibit precipitation of scale, particularly phosphate scale, by threshold inhibition. That application discloses effectiveness of the copolymers against calcium phosphate, calcium carbonate, calcium sulfate, and magnesium hydroxide. At middle of page 5 of that application, other scale or precipitates are noted, including iron oxide.
It should be understood that the iron oxide referred to in U.S. Pat. No. 4,566,973 is in a solid, particulate form and that the function of the copolymers relative to iron oxide, and like materials, is that of suspending agents. The function of such suspending agents is to disperse and maintain the iron oxide particles dispersed so that they do not precipitate or deposit on internal surfaces of equipment containing the aqueous medium.
The invention herein pertains to the use of same and similar copolymers to maintain solubilized ferric ions in solution so that they do not form precipitates which would deposit on surfaces of equipment. The copolymers function as stabilizing agents towards soluble iron or ferric ions and maintain such ions in solution.